<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php
// traditional (any PHP)
putenv('TZ=Europe/Copenhagen');
function findweekdate1($y, $w, $d) {
    $target = "$y $w $d";
    $t = mktime(12, 0, 0, 12, 29, $y-1);
    $t += (($w - 1)*7*24*60*60);
    for($i = 0; $i < 14; $i++) {
        if(date('o W N', $t) == $target) {
                        return $t;
        }    
        $t += (24*60*60);
    }
    return 0;
}

$res = findweekdate1(2009, 33, 1);
echo date('d/m/Y', $res) . "\r\n";
$res = findweekdate1(2009, 63, 1);
echo date('d/m/Y', $res) . "\r\n";

// OOP (PHP 5.2+)
date_default_timezone_set('Europe/Copenhagen');
$dt = new DateTime();

$dt->setISODate(2009, 33, 1);
echo $dt->format('d/m/Y') . "\r\n";
$dt->setISODate(2009, 63, 1);
echo $dt->format('d/m/Y') . "\r\n";

// alternative (newer PHP, possible 5.1+)
date_default_timezone_set('Europe/Copenhagen');
function findweekdate2($y, $w, $d) {
    return strtotime("$y-W$w-$d");
}

$res = findweekdate2(2009, 33, 1);
echo date('d/m/Y', $res) . "\r\n";
$res = findweekdate2(2009, 63, 1);
echo date('d/m/Y', $res) . "\r\n";
?>